This invention relates to the preparation of iridium- and platinum-containing films on substrates, particularly on semiconductor device structures.
Films of metals and metal oxides, particularly the heavier elements of Group VIII, are becoming important for a variety of electronic and electrochemical applications. For example, high quality RuO2 thin films deposited on silicon wafers have recently gained interest for use in ferroelectric memories. Many of the Group VIII metal films are generally unreactive toward metal oxides, resistant to diffusion of oxygen and silicon, and are good conductors. Oxides of certain of these metals also possess these properties, although perhaps to a different extent.
Thus, films of Group VIII metals and metal oxides, particularly the second and third row metals (e.g., Ru, Os, Rh, Ir, Pd, and Pt) have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for electrical contacts. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories. Furthermore, they may even be suitable as the plate (i.e., electrode) itself in capacitors. Iridium oxide is of particular interest as a barrier layer because it is very conductive (30-60 xcexcxcexa9-cm) and is inherently a good oxidation barrier.
Capacitors are the basic charge storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs). It is important for device integrity that oxygen and/or silicon not diffuse into or out of the dielectric material. This is particularly true for ferroelectric RAMs because the stoichiometry and purity of the ferroelectric material greatly affect charge storage and fatigue properties.
The electrodes in a DRAM cell capacitor must protect the dielectric layer from interaction with surrounding materials, including interlayer dielectrics (e.g., BPSG), and from the harsh thermal processing encountered in subsequent steps of DRAM process flow. In order to finction well as a bottom electrode, the electrode layer or layer stack acts as an effective barrier to the diffusion of oxygen and silicon. Oxidation of the underlying silicon will result in decreased series capacitance, thus degrading the cell capacitor. Platinum is one of the candidates for use as an electrode material for high dielectric capacitors.
Platinum, alone, however, is relatively permeable to oxygen. One solution is to combine (e.g., alloy) the platinum with rhodium to enhance the barrier properties of the layer. Physical vapor deposition (PVD) of a Ptxe2x80x94Rh alloy has been shown by H. D. Bhati et. al., xe2x80x9cNovel high temperature multi-layer electrode barrier structure for high-density ferroelectric memories,xe2x80x9d Applied Physics Letters, 71, pp. 719-21 (1997), to provide an improvement over pure Pt for electrode applications. Also, physical vapor deposition (PVD) of a Ptxe2x80x94Ir alloy has been shown in JP 09162372.
Many storage cell capacitors are formed using high aspect ratio openings. PVD deposition (e.g., sputtering) does not deliver a layer which is sufficiently conformal for formation of an electrode within such a small high aspect ratio opening.
Thus, there is a continuing need for methods and materials for the deposition of metal-containing films, such as iridium- and platinum-containing films, which can function as barrier layers, for example, in integrated circuits, particularly in random access memory devices.
The present invention is directed to methods for forming films, particularly in the manufacture of a semiconductor device, such as a ferroelectric device, and devices (e.g., capacitors, integrated circuit devices, and memory cells) containing such films. The methods involve forming films containing both iridium and platinum on substrates, such as semiconductor substrates or substrate assemblies during the manufacture of semiconductor structures. The film can be a pure platinum-iridium film, an oxide film, a sulfide film, a sulfide film, a selenide film, a nitride film, or the like. Typically and preferably, the iridium- and platinum-containing film (i.e., platinum-iridium film) is electrically conductive. The resultant film can be used as a barrier layer or electrode in an integrated circuit structure, particularly in a memory device such as a ferroelectric memory device. The platinum-iridium film (i.e., layer) overcome some of the problems associated with the use of platinum alone as an electrode material.
In the context of the present invention, the term xe2x80x9cmetal-containing filmxe2x80x9d includes, for example, relatively pure films of iridium and platinum (typically, in the form of alloys or solid solutions), as well as mixtures or alloys with other Group VIII transition metals such as rhodium, nickel, palladium, iron, ruthenium, and osmium, metals other than those in Group VIII, metalloids (e.g., Si), or mixtures thereof. The term also includes complexes of iridium and platinum with other elements (e.g., O, N, and S).
One preferred method of the present invention involves forming a film on a substrate, such as a semiconductor substrate or substrate assembly during the manufacture of a semiconductor structure. The method includes: providing a substrate (preferably, a semiconductor substrate or substrate assembly); providing a precursor composition that includes one or more complexes of the formula:
LyIrYz,xe2x80x83xe2x80x83(Formula I)
wherein: each L group is independently a neutral or anionic ligand; each Y group is independently a pi bonding ligand selected from the group of CO, NO, CN, CS, N2, PX3, PR3. P(OR)3, AsX3, AsR3, As(OR)3, SbX3, SbR3, Sb(OR)3, NHxR3xe2x88x92x, CNR, and RCN, wherein R is an organic group and X is a halogen; y=1 to 4; z=1 to 4; x=0 to 3; providing a precursor composition that includes one or more platinum complexes; and forming a platinum-iridium-containing film from the precursor compositions on a surface of the substrate (preferably, the semiconductor substrate or substrate assembly), wherein the platinum-iridium-containing film has the formula platinum(x):iridium(1xe2x88x92x), wherein x is in the range of about about 0.99 to about 0.01. Preferably, the precursor composition that includes one or more complexes of the formula LyIrY2 is the same as the precursor composition that includes one or more platinum complexes.
In certain embodiments, the process is carried out in a nonhydrogen atmosphere (i.e., an atmosphere that does not include H2). In other embodiments, preferably Y and L do not include halogen atoms, and more preferably, L is not a cyclopentadienyl ligand when Y is a CO ligand. Using such methods, the complexes of Formula I are converted in some manner (e.g., decomposed thermally) and deposited on a surface to form a metal-containing film. Thus, the film is not simply a film of the complex of Formula I.
Preferably, the precursor complexes are neutral complexes and may be liquids or solids at room temperature. Typically, however, they are liquids. If they are solids, they are preferably sufficiently soluble in an organic solvent or have melting points below their decomposition temperatures such that they can be used in flash vaporization, bubbling, microdroplet formation techniques, etc. However, they may also be sufficiently volatile that they can be vaporized or sublimed from the solid state using known vapor deposition techniques including chemical vapor deposition and atomic layer deposition techniques. Thus, the precursor compositions of the present invention can be in solid or liquid form. As used herein, xe2x80x9cliquidxe2x80x9d refers to a solution or a neat liquid (a liquid at room temperature or a solid at room temperature that melts at an elevated temperature). As used herein, a xe2x80x9csolutionxe2x80x9d does not require complete solubility of the solid; rather, the solution may have some undissolved material, preferably, however, there is a sufficient amount of the material that can be carried by the organic solvent into the vapor phase for chemical vapor deposition processing.
The methods described herein preferably involve the use of vapor deposition techniques such as chemical vapor deposition and atomic layer deposition, although this is not a requirement for all embodiments.
The present invention also provides a capacitor. In one embodiment, the capacitor includes: a first conductive layer; a dielectric material on at least a portion of the first conductive layer; and a second conductive on the dielectric material; wherein at least one of the first and second layers includes a vapor-deposited platinum-iridium film (i.e., a film deposited by vapor deposition methods that includes platinum and iridium, preferably in the form of an alloy). Another embodiment of a capacitor includes: a first conductive layer; a dielectric material on at least a portion of the first conductive layer; and a second conductive layer on the dielectric material; and a conductive barrier layer that includes a vapor-deposited platinum-iridium film. In this latter embodiment, preferably, the first conductive layer forms an electrode and is interposed between the dielectric material and the barrier layer. Preferably, the barrier layer is interposed between the dielectric material and the first conductive layer.
The present invention also provides an integrated circuit that includes a capacitor. In one embodiment, the capacitor includes: a first conductive layer; a dielectric material on at least a portion of the first conductive layer; and a second conductive layer on the dielectric material; wherein at least one of the first and second conductive layers includes a vapor-deposited platinum-iridium film. In another embodiment, the capacitor includes: a first conductive layer; a dielectric material on at least a portion of the first conductive layer; a second conductive layer on the dielectric material; and a conductive barrier layer that includes a vapor-deposited platinum-iridium film. In this latter embodiment, preferably, the first conductive layer forms an electrode and is interposed between the dielectric material and the barrier layer. Preferably, the barrier layer is interposed between the dielectric material and the first conductive layer.
The present invention also provides a memory cell. In one embodiment, the memory cell includes: a transistor; and a capacitor that includes a barrier layer that includes a vapor-deposited platinum-iridium film. Preferably, the capacitors are as described above.
The present invention also provides methods of fabricating capacitors. In one embodiment, a method involves: forming a first conductive layer; forming a dielectric layer on at least a portion of the first conductive layer; and forming a second conductive layer on the dielectric layer; wherein at least one of the first and second conductive layers includes a vapor-deposited platinum-iridium film. Preferably, the conductive barrier layer is formed by chemical vapor co-deposition of platinum and iridium precursor compositions. In another embodiment, a method for fabricating a capacitor involves: forming a first conductive layer; forming a dielectric layer on at least a portion of the first conductive layer; forming a second conductive layer on the dielectric layer; and forming a conductive barrier layer that includes a vapor-deposited platinum-iridium film. Preferably, the first conductive layer is interposed between the barrier layer and the dielectric layer. Preferably, the second conductive layer is interposed between the barrier layer and the dielectric layer.
In another embodiment of a method for fabricating a capacitor having a first and a second electrode, the method includes: providing a substrate; forming an insulative layer overlying a substrate; forming an opening in the insulative layer to expose the substrate; forming a conductive plug in the opening, the conductive plug forming a first portion of the first electrode of the capacitor, the conductive plug recessed below a surface of the insulative layer; forming a first conductive layer in the opening and overlying the conductive plug such that the first conductive layer is surrounded on sidewalls by the insulative layer, the first conductive layer forming a second portion of the first electrode, the first conductive layer being formed of a vapor-deposited platinum-iridium film; and forming a second conductive layer overlying the first conductive layer, the second conductive layer forming a third portion of the first electrode. Preferably, the method further includes: creating a dielectric layer on the second conductive layer, the first conductive layer substantially preventing oxidation of the dielectric layer; and creating the second electrode overlying the dielectric layer, the first and the second electrode and the dielectric layer forming the capacitor. Preferably, forming the second electrode includes sputtering an electrically conductive material to overly the dielectric layer. Preferably, forming the first conductive layer includes: admitting a platinum precursor composition to a chemical vapor deposition reaction chamber; admitting an iridium precursor composition to the chemical vapor deposition reaction chamber; and applying sufficient reaction gas to the chemical vapor deposition reaction chamber to cause co-deposition of platinum and iridium. Preferably, the method further includes planarizing the insulative layer prior to forming the conductive plug. Preferably, forming the conductive plug includes depositing in-situ doped polysilicon in the opening.
Preferably, in the methods and articles described herein, the platinum-iridium films (preferably, in the form of alloys or solid solutions) have the formula platinum(x):iridium(1xe2x88x92x), wherein x is in the range of about 0.99 to about 0.01. Preferably, the dielectric layer is selected from the group consisting of tantalum pentoxide (Ta2O5), Barium Strontium Titanate (BST), Strontium Titanate (ST), Lead Zirconium Titanate (PZT), Strontium Bismuth Tantalate (SBT) and Bismuth Zirconium Titanate (BZT).
In the methods described herein, preferably, the platinum precursor composition includes a platinum complex selected from the group consisting of CpPt(Me)3, wherein Me is a methyl group and Cp is substituted or unsubstituted cyclopentadienyl, Pt(CO)2Cl2, cis-Pt(CH3)2[(CH3)NC]2, (COD)Pt(CH3)2, (COD)Pt(CH3)Cl, (C5H5)Pt(CH3)(CO), (acac)(Pt)(CH3)3, Pt(acac)2, Pt(PF3)4, wherein COD=1,5 cycloctadiene and acac=acetylacetonate, and mixtures thereof. More preferably, the platinum precursor composition includes CpPt(Me)3, wherein Me is a methyl group and Cp is methyl cyclopentadienyl. Preferably, the platinum complexes do not include halogen atoms.
In the methods described herein, preferably the iridium precursor composition includes one or more complexes of Formula I above. More preferably, the iridium precursor has the formula: LyIrYz, wherein: each L group is independently a neutral or anionic ligand; each Y group is independently a pi bonding ligand selected from the group of CO, NO, CN, CS, N2, PR3, P(OR)3, AsR3, As(OR)3, SbR3, Sb(OR)3, NHxR3xe2x88x92x, CNR, and RCN, wherein R is an organic group, and x=0 to 3; y=1 to 4; and z=1 to 4.
Methods of the present invention are particularly well suited for forming films on a surface of a semiconductor substrate or substrate assembly, such as a silicon wafer, with or without layers or structures formed thereon, used in forming integrated circuits. It is to be understood that methods of the present invention are not limited to deposition on silicon wafers; rather, other types of wafers (e.g., gallium arsenide wafer, etc.) can be used as well. Also, the methods of the present invention can be used in silicon-on-insulator technology. Furthermore, substrates other than semiconductor substrates or substrate assemblies can be used in methods of the present invention. These include, for example, fibers, wires, etc. If the substrate is a semiconductor substrate or substrate assembly, the films can be formed directly on the lowest semiconductor surface of the substrate, or they can be formed on any of a variety of the layers (i.e., surfaces) as in a patterned wafer, for example. Thus, the term xe2x80x9csemiconductor substratexe2x80x9d refers to the base semiconductor layer, e.g., the lowest layer of silicon material in a wafer or a silicon layer deposited on another material such as silicon on sapphire. The term xe2x80x9csemiconductor substrate assemblyxe2x80x9d refers to the semiconductor substrate having one or more layers or structures formed thereon.